MIC2225 Datasheet, PDF (11/14 Pages) Micrel Semiconductor – 2MHz 600mA Synchronous Buck Regulator with 300mA LDO

Micrel, Inc.
Application Information
The MIC2225 is a 600mA PWM and 300mA LDO dual
power supply. Both PWM output and LDO outputs are
independent and are controlled by EN and ENLDO pins
respectively. These enable pins are logic level
compatible.
Input Capacitor
A minimum 1µF ceramic is recommended on the VIN pin
for bypassing. X5R or X7R dielectrics are recommended
for the input capacitor. Y5V dielectrics loose most of
their capacitance over temperature and are therefore,
not recommended.
A minimum 1µF is recommended for placement close to
the VIN and PGND pins for high frequency filtering.
Smaller case size capacitors are recommended due to
their lower ESR and ESL. Please refer to layout
recommendations for proper layout of the input
capacitor.
Output Capacitor
Even though the MIC2225 is optimized for a 2.2µF
output capacitor, output capacitance can be varied from
1µF to 10µF. The MIC2225 utilizes Type III internal
compensation and utilizes an internal high frequency
zero to compensate for the double pole roll off of the LC
filter. For this reason, larger output capacitors can create
instabilities. X5R or X7R dielectrics are recommended
for the output capacitor. Y5V dielectrics lose most of
their capacitance over temperature and are therefore,
MIC2225
not recommended.
In addition to a 2.2µF, a small 10nF is recommended
close to the load for high frequency filtering. Smaller
case size capacitors are recommended due to there
lower ESR and ESL.
Inductor Selection
The MIC2225 is designed for use with a 2.2µH inductor.
Proper selection should ensure that the inductor can
handle the maximum average and peak currents
required by the load. Maximum current ratings for the
inductor are generally given in two methods; permissible
DC current and saturation current. Permissible DC
current can be rated either for a 40°C temperature rise
or a 10% to 20% loss in inductance. Ensure that the
inductor selected can handle the maximum operating
current. When saturation current is specified, make sure
that there is enough margin so that the peak current will
not saturate the inductor. Peak inductor current can be
calculated as follows:
I_PK
= I_OUT
+
V_{OUT ⎜⎜⎝⎛}1 −
V_OUT
V_IN
2×f ×L
⎟⎟⎠⎞
October 2007
11
M9999-101107-B